Automotive manufacturers and the National Highway Transportation Safety Association are investigating methods to disable vehicle air bags in situations where they may cause more harm than good. Typically, airbags have been developed to deploy with enough force to restrain a 175 lb. adult in a high velocity crash. Deployment of the same air bags when infants or children are seat occupants may cause serious injury due to the force generated upon inflation of the bag. This invention can be used to disable a passenger side air bag when infants or children are present in the passenger seat.
Another potentially harmful occupant seating situation is when the occupant is in close proximity to the air bag inflator door at the time of air bag deployment. Recent National Highway Transportation Safety Association data suggests that severe injuries caused by the air bag can be minimized or eliminated if the air bag is disabled when the occupant is closer than approximately four inches from the inflator door. The present invention may be used to detect a human body part that is within a "danger zone" around the air bag inflator assembly at the time of impact such that the air bag could be disabled or its inflation profile could thereby be reduced. Furthermore, the invention can be used to disable the passenger side air bag in nearly all occupant seating situations where air bag deployment is hazardous.
The present invention comprises a seat weight sensor, a seat belt tension sensor, and a capacitive sensor located in the instrument panel or dashboard near the air bag inflator door for sensing the proximity of a human to the air bag deployment danger zone.
The seat weight sensor and the seat belt tension measurement sensor are employed in concert to determine if the occupant is large enough for safe air bag deployment. The capacitive sensor operates independently of the aforementioned sensors to disable the air bag when a human presence is detected too close to the air bag inflator door just prior to air bag deployment.
Seat weight sensors are being developed to determine when the passenger seat occupant is sufficiently small to require the disablement of an air bag inflator. Such sensors should ideally be capable of determining when the child is in a rear facing infant seat, a forward facing child seat or a booster seat. Occupant weight measurement in child seat occupant situations is complicated by the force exerted downwardly on the seat by seat belt tension. A tightly belted child seat increases the measured weight or force exerted on the seat, possibly causing air bag deployment on children or infants.
Prior art systems using multiple sensor technologies have been developed to inhibit air bag deployment in dangerous situations. Sensors such as infra-red sensors, passive infra-red sensors (heat detectors), ultrasonic sensors, capacitive sensors, weight sensors, and child seat "tag" sensors have previously been employed. A plurality of the aforementioned sensors have been used together in an attempt to identify child seats, small occupants, empty seats, large occupants and out-of-position occupants. Generally, the greater number of sensors employed, the better the system performance. However, the cost of systems that use numerous sensors is prohibitive and vehicle assembly is complex.
The instant invention incorporates a belt tension measurement system to identify the situations where child seats are belted tightly to the seat. Since normally seated adults are generally uncomfortable when seat belt tension exceeds ten pounds, a seat belt tension measurement greater than ten pounds indicates that the occupant is not a normally seated adult. In the aforementioned situation where the seat belt is under high tension, the air bag is safely disabled.
Correspondingly, when the seat belt tension is low, the force exerted on the seat as measured by the weight sensor is not greatly influenced by seat belt tension thereby allowing the weight sensor measurement to determine the weight of the occupant. Where low belt tension exists, the air bag is enabled when a relatively large weight is present and disabled when a weight below a predetermined threshold is sensed. An air bag having variable inflation characteristics can be tailored to inflate at a rate corresponding to the measured weight of the occupant.
Air bags can also prove hazardous to passengers located too close to the inflator at the time of vehicle impact, particularly where the occupant is unbelted and experiences severe pre-impact braking. A capacitive, or electric field, sensor detects the presence of a passenger near the inflator door quickly enough to disable the air bag while the passenger is still "flying" through the air during a pre-impact breaking event, thereby protecting an out of position occupant from the force generated by air bag deployment.